The present invention relates to a coated bearing manufacturing method of and a coated bearing manufacturing apparatus for forming a coating layer on a bearing base material, and more particular, to a method of and an apparatus for forming a coating layer on an inner surface of a cylindrical-shaped or semicylindrical-shaped bearing base material with the use of a coating roll.
Ordinarily, a coating layer of a coated bearing is formed by using a coating liquid obtained by mixing a thermosetting resin such as polyimide resin (PI), epoxy resin, phenol resin, etc. with a solid lubricant such as molybdenum disulfide (MoS2), graphite (Gr), etc. and applying the coating liquid to an inner surface of a bearing base material.
Ways to apply a coating liquid to an inner surface of a bearing base material include a spraying method or a printing method. The spraying method comprises jetting a coating liquid in a foggy manner from a spraying device to apply the same to an inner surface of a bearing base material and the printing method comprises using a pad or a roll to apply a coating liquid to an inner surface of a bearing base material.
JP-A-2001-304264 discloses a method of forming a coating layer on an inner surface of a half bearing in printing (referred below to as rolling printing), in which a roll is used. In the method, there are provided a transfer roll, a coating roll (printing roll), and a backup roll. In order to form a coating layer, a coating liquid is first dropped on a roll surface of a transfer roll and a coating roll is rotationally brought into contact with the transfer roll whereby the coating liquid is transferred in uniform thickness to the coating roll. Succeedingly, a half bearing (bearing base material) is interposed between the coating roll and the backup roll and the both rolls are rotated. Thereby, the bearing base material passes between the both rolls and in the passing process, the coating liquid on the coating roll is applied to an inner surface of the half bearing.
The spraying method involves a large dispersion in created film thickness and an amount of a coating liquid, which is scattered and wasted, is much since the coating liquid is jetted in a foggy manner from the spraying device. In the printing method, an amount of a coating liquid wasted as in the spraying method can be made small. In the printing method, in which a pad is used, however, a coating layer is bad in thickness accuracy since the pad is pushed against an inner surface of a half bearing to apply a coating liquid thereto.
The printing method, in which a roll is used, shown in JP-A-2001-304264 is excellent in thickness accuracy as compared with the pad printing. In the rolling printing method in JP-A-2001-304264, a transfer roll and a coating roll are rotationally brought into contact with each other, that is, contact pressure between the transfer roll and the coating roll causes a coating liquid to spread over a surface of the coating roll. In a system, in which contact pressure between the both rolls causes a coating liquid to spread, however, it is difficult to control a coating liquid to make the same constant in thickness over a whole periphery of the coating roll. Therefore, in the case where the coating liquid spread over a surface of the coating roll is applied to an inner surface of a half bearing to form a coating layer, the coating layer is liable to become ununiform in thickness.
Also, in order to interpose a half bearing between a coating roll and a backup roll to apply a coating to an inner surface of the half bearing, it is necessary to separate the coating roll from a transfer roll to move the same near the backup roll. When the coating roll is separated from the transfer roll, however, a coating liquid, is drawn to a portion thereof, which has been in contact with the transfer roll, to stay there with the result that there is caused a problem that in case of applying a coating liquid to a half bearing, a coating layer becomes locally and partially large in thickness.